1. Field of the Invention
This invention relates to metallurgical furnaces of the type used to reheat metal prior to hot working, wherein certain water-cooled furnace members are covered with refractory material so as to insulate and protect them from hot furnace gases.
2. Description of Related Art
Furnaces for heating metal during processing often operate at temperatures up to about 2400xc2x0 F. At such elevated temperatures it is necessary to protect furnace structural members from such intense heat. Furnace members providing support for heavy metal sections, such as billets or slabs being heated in such furnaces, are insulated and are cooled internally with circulating fluid so as to maintain the strength required to support the weight of the heavy metal sections.
Furnace support members for heavy metal sections, commonly referred to as skid rails, typically consist of horizontally oriented water cooled pipes having an upwardly projecting wear surface along their length. The heavy metal sections, which are to be heated, are slid along the wear surfaces of such support members as they move from the furnace entrance to the furnace exit. Insulation for the support members is commonly of a single refractory material or can be made up of concentric layers of different materials and are referred to as refractory tiles. A multitude of different means are employed to secure the refractory tiles to the furnace members in a manner to withstand the high temperature, thermal shock, vibration, and other forces to which the furnace members and refractory tiles are subjected. Relative ease of installation is of importance, due to the requirement for periodic replacements.
U.S. Pat. No. 4,424,027 describes a refractory tile in which an access hole is provided for use in welding an embedded channel to a fluid cooled furnace member with the use of a mig-welder.
U.S. Pat. No. 3,881,864 describes a refractory tile surrounding an inner fibrous refractory material about a furnace skid rail wherein two complimentary c-shaped blocks inter-engage beneath the skid rail to secure the insulation in place. No additional means is provided for attachment.
U.S. Pat. No. 4,393,569 describes a module wherein the support member is wrapped with refractory fiber insulating material which is protected by an outer refractory ceramic fiber blanket which is folded into at least two layers.
U.S. Pat. No. 4,140,484 describes a tubular supporting member sheathed by refractory sheathing comprising an inner layer of fibrous refractory material and an outer layer of refractory tiles held in place by metal links which are secured together around the supporting members.
U.S. Pat. No. 4,071,311 describes a metal tubular supporting member sheathed by an inner layer of refractory fibrous material and an outer layer consisting of pairs of semi-cylindrical refractory tiles. The refractory tiles are held in place by metal coupling links covered and positively engaged by adjacent tiles.
U.S. Pat. No. 4,015,636 describes a three-layer insulating assembly comprising an inner fibrous thermal insulation, an intermediate split ceramic refractory, and an outer protective ceramic covering.
U.S. Pat. No. 4,450,872 describes a covering comprising an inner layer of thermal insulating ceramic refractory fiber blanket, an open weave ceramic cloth about the blanket, an inner layer of veneering mortar, compressed rings of ceramic fiber material, and a hot face layer of veneering coating.
U.S. Pat. No. 3,881,864 describes a refractory tile for sheathing a furnace member, preferably around an inner layer of fibrous refractory material. xe2x80x9cCxe2x80x9d shaped complimentary tiles inter-engage each other underneath the member to hold them in position.
In an improvement over refractory tiles having insulation in concentric layers of different materials, U.S. Pat. No. 6,179,619 describes a composite refractory tile for metallurgical furnace members having layered refractory materials wherein a cast refractory material extends from the furnace member being insulated, to an external surface of the refractory tile at selected portions of the tile located at individual attachment means and near ends of each tile. The composite refractory tile of U.S. Pat. No. 6,179,610 is shown in FIG. 13, in a cross-sectional view perpendicular to a longitudinal direction of the tile. The view is taken in a portion of the tile in which an attachment means is provided. In FIG. 14, the same composite refractory tile is shown in a cross-sectional view in a plane which includes the longitudinal axis 108 of the tile. In FIGS. 13 and 14, water cooled member 101 is insulated with composite refractory tile sections 102, 102 which are made up of cast refractory portions 103 and insulating ceramic fiber blanket portions 104. In the portions surrounding a metal attachment means 105, the cast refractory material extends continuously from fluid-cooled furnace member 101 to outer surface 106 of the tile. Each of the metal attachment means 105 is independent of any of the other attachment means as far as any rigid metal connecting means is concerned. The attachment means can be welded to the fluid cooled furnace member 101 with use of a mig-welder, with access through access holes 107.
In the composite refractory tile of U.S. Pat. No. 6,179,610, the superior insulating properties of the ceramic fiber blanket 104 are utilized in all portions of the tile in which the superior rigidity properties of the cast refractory 103 are not needed. The cast refractory 103 is relied on for centering the tile 102 on the cooled furnace member 101 and for providing a location for embedding anchoring wires 109 which are part of the attachment means 105 which are relied on for holding the tile 102 in place on furnace member 101. In the preferred method of installation welding base 110 of attachment means 105 is welded to furnace member 101. Anchoring wires 109 are attached to welding base 110 through flat washer 111.
As shown in FIG. 13, the anchoring wires 109 extend, in the cast refractory material, radially away from furnace member 101, and then extend in the longitudinal direction of the furnace member. As shown in FIG. 14, other anchoring wires 109 extend, in the cast refractory material, radially away from furnace member 101, and then in a direction generally perpendicular to the longitudinal direction of the furnace member.
As can be seen in FIGS. 13 and 14, end portions of the anchoring wires 109 are disposed in the cast refractory portions which have the better insulating ceramic fiber blanket 104 disposed radially inward. It has been found that having the end portions of the anchoring wires 109 at those locations subjects those end portions to higher temperatures than portions of the anchoring wires which have the cast refractory material disposed radially inward the entire distance from the outer surface 106 of the tile 102, to the inner surface of the tile which contacts the furnace member 101, such as at 113 and 114 of FIG. 13 and FIG. 14 respectfully. Exposure of the anchoring wires to a higher temperature, and the differential in temperature along the length of the anchoring wires lead to a decrease in the useful life of the composite refractory tile.
It is an object of the present invention to provide a composite refractory tile in which the temperature of the anchoring wire is at a reduced temperature (relative to an anchoring wire of the above-described prior art tile installed in a furnace operating at the same temperature), and to reduce the difference in temperature along the length of the anchoring wire.
The present invention provides a pair of composite refractory tiles for insulating fluid-cooled structural members of a metallurgical furnace. Each tile has a rigid cast refractory shell adapted to be disposed about a portion of the fluid-cooled furnace member, with the shell having an inner face and an opposed outer face, opposed end walls corresponding to the longitudinal direction of the elongated fluid-cooled furnace member, and two edge walls extending between the end walls. The inner face has selected portions for contacting the fluid-cooled furnace member, and remaining portions for being radially spaced from the fluid-cooled furnace member and thereby defining a hollow. A ceramic fiber blanket is disposed within the hollow, the material of the ceramic fiber blanket having a higher insulating k value than material of the cast refractory shell. At least one attachment means is disposed in selected portions of the rigid cast refractory shell, each of the attachment means is so constructed and arranged so as to be disposed within portions of the cast refractory shell having temperatures lower, when in use, than temperatures of remaining portions which are radially spaced from the fluid-cooled furnace member and have the ceramic fiber blanket disposed in the defined hollow.